The present invention is directed to a self-configuring controller for a heating, ventilating and air conditioning system (HVAC system) and, more particularly, to a method and apparatus for accurately, automatically, and continually configuring the controller of the HVAC system to select the optimal operating mode for the current system configuration.
Large scale HVAC systems are tailored to the owner's specific needs and requirements. An HVAC system will typically include one or more compressors, one or more condensers, one or more evaporators, and one or more condenser fans, all of which are controlled by a controller. The HVAC system can also include an economizer, heat pump operation, a building automation system, and a heating system. The controller is generally provided to monitor and control the operation of the system as configured by the owner of the HVAC system.
Many problems which are found in prior systems result from human error in programming or identifying the system configuration to the controller. Other problems occur because the system configuration changes due to component failure or recovery, or to modification of the system by the owner.
Prior art systems have relied on configuration jumpers and DIP switches to initially inform the controller of the system's configuration. Configuration jumpers are a series of paired input terminals which are individually connected or disconnected by an installer to inform the controller of the presence or absence of particular system elements or functions. Similarly, a DIP (dual in-line package) switch is a bank of small switches adapted for easy insertion into a printed circuit board. The individual switches of the DIP switch are opened or closed by an installer to provide an input to the controller representative of the presence or absence of particular system functions or elements. However, both configuration jumpers and DIP switches are subject to installer error during the initial system configuration, and both are subject to accidental alteration once the system has been established. Additionally, DIP switches have been known to be install backwards, leading to additional errors.
U.S. Pat. No. 4,545,210 to Lord shows an electronic program control including programmable headers with fixed jumpers which develop a binary code to configure a microprocessor to the physical characteristics of an assembled refrigeration unit. The programmable header is programmed at the factory by selectively breaking the jumpers to develop the binary code. Programming of the microprocessor for accessory equipment can be performed by field service personnel using small dip switches to develop a binary code for the microprocessor. Both dip switches and the selectively broken jumpers of the programmable header are subject to considerable human error in determining the physical characteristics of the assembled refrigeration unit and the accessory equipment. Additionally, programmable headers require considerable design effort in laying out the configuration of the controller, to ensure that there exists a single location containing all of the connections to the programmable header, and all of the connections to the dip switches. Furthermore in addition to the cost and limitations of such a design effort, the cost of the programmable headers, the fixed jumpers, the connections, and the dip switches can add considerable expense to a controller.
Once the HVAC system has been initially configured, and is operating, further problems occur. In existing systems, the failure of an input such as a sensor due to a lack of a signal or to an out of range signal typically results in a system shutdown or in diminished, inaccurate operation. Essentially, previous approaches to operational failures use a fail safe approach. In a fail safe approach a predetermined default mode is used without regard to whether the component which actually failed effects the mode of operation being used. No attempt is made to determine and to continue to operate in the best available mode of operation possible without the failed component.
U.S. Pat. No. 4,598,355 to Shepler et al. shows a fault tolerant controller which includes means for detecting a fault in the controller or in an output device. The output device is controlled in a fail safe mode of operation wherein any type of failure results in a mode of operation which controls the output device as if the controller was not present in the system. A return to the normal mode of operation is caused only if the fault ceases to exist while in the fail safe mode of operation. This patent makes no attempt to continue to operate in the best available mode of operation. Additionally, the fail safe mode of operation is limited to output device failures. When the controller itself or one of its primary functions experiences a failure, a permanent fail safe flag is set ton indicate a non-recoverable type error.
U.S. Pat. No. 4,432,210 to Saito shows an air conditioning control method for setting the desired outlet air temperature in response to abnormal sensor inputs. The method selects one of a plurality of fail safe calculation formulae, the selected formulae being one which does not employ any of the abnormal sensor inputs. The mode of operation does not change. Only the outlet air temperature setting varies in response to an abnormal sensor input.
U.S. Pat. No. 4,535,598 to Mount shows a method and control system for a refrigeration system which aborts the start up of the refrigeration system if a signal provided by a sensor is not within normal limits prior to start up. Additionally, the control system shuts down the operation of the refrigeration system if the system verifies an out of bounds signal provided by the sensor during the operation of the refrigeration system. No attempt is made to continue to operate the system in any other mode of operation.
U.S. Pat. No. 4,682,279 to Watabe shows an operating mode selector which selects between cooling, shut down, and heating modes of operation by determining whether a temperature T sensed by a temperature sensor is within upper and lower preset limits. The selected operational mode is maintained as long as the sensed temperature is within the upper and lower limits. A new mode of operation is selected when the sensed temperature exceeds the preset limits of the previous mode of operation. Component failure or invalid input signals are not contemplated.
U.S. Pat. No. 4,381,549 shows a microprocessor controlled apparatus for automatically diagnosing faults in a heat pump system. As long as any one indoor temperature sensor operates properly, the system will continue to operate properly. When all temperature sensors fail, a fault condition arises. However, neither a fault condition nor the failure of individual sensors results in a change in the mode of operation.
U.S. Pat. No. 4,333,316 shows a heat pump control apparatus in which normal target temperature settings are automatically converted to an expanded operating temperature range in response to a predetermined number of invalid data signals. Again, the mode of operation is not changed.
U.S. Pat. No. 4,580,947 to Shibata et al. shows a method of controlling the operation of a plurality of compressors. The method attempts to prolong the life of the compressors by stopping the compressor which has worked the longest whenever the system load decreases, and starting a compressor other than the compressor working the longest whenever the system load is increasing.